JP7620539B2 - Fuel Cell Systems - Google Patents

Description

An embodiment of the present invention relates to a fuel cell system.

The fuel cell stack comprises a laminate in which multiple single cell batteries are stacked. The laminate has flow paths for fuel gas, oxidant gas, and coolant. The fuel cell stack generates electricity through an electrochemical reaction between the fuel gas and oxidant gas introduced into the laminate. Cooling water is also introduced into the laminate to cool the heated stack. As shown in JP 2014-049267 A, the cooling water that has cooled the stack is discharged from the fuel cell stack using a cooling water pump. The cooling water pump is disposed downstream of the fuel cell stack in the direction of the flow of the cooling water.

Here, the cooling water discharged from the fuel cell stack may contain air bubbles. If cooling water containing air bubbles is introduced into the cooling water pump, the operating efficiency of the cooling water pump may decrease. As a result, cooling water may not be supplied sufficiently to the fuel cell stack, and the fuel cell stack may not be cooled sufficiently. If the fuel cell stack cannot be cooled sufficiently, the performance of the fuel cell stack may be impaired. To solve this problem, an air bleed valve is provided at the cooling water inlet of the cooling water pump to release the air bubbles in the cooling water into the atmosphere and suppress the introduction of air bubbles into the cooling water pump.

JP 2014-049267 A

However, when the pressure in the cooling water flow path is lower than atmospheric pressure, it is difficult for the air bleed valve to release the air bubbles in the cooling water into the atmosphere. For this reason, a special pump must be used as the cooling water pump. Such pumps are expensive, which increases the installation costs of the fuel cell system.

The present invention was made in consideration of these points, and aims to provide a fuel cell system that can bleed air from the cooling water even when the pressure in the cooling water flow path is lower than atmospheric pressure.

The fuel cell system according to the embodiment includes:
a fuel cell stack that generates electricity using hydrogen and oxygen;
a cooling water discharge pipe connected to the fuel cell stack;
a cooling water pump that discharges cooling water from the fuel cell stack through the cooling water discharge pipe;
Equipped with
During operation of the cooling water pump, the pressure in the cooling water discharge pipe is lower than atmospheric pressure at least between the fuel cell stack and the cooling water pump;
An air vent pipe extending generally in a vertical direction is connected to the cooling water discharge pipe between the fuel cell stack and the cooling water pump.

According to the fuel cell system of the embodiment, it is possible to bleed the air from the cooling water even when the pressure in the cooling water flow path is lower than atmospheric pressure.

FIG. 1 is a diagram showing the configuration of a fuel cell system according to an embodiment. FIG. 2 is a diagram for explaining the flow of fluid within the fuel cell stack shown in FIG. FIG. 3 is a cross-sectional view taken along line III-III of the laminate of the fuel cell stack shown in FIG. FIG. 4 is a flowchart for explaining a control method for the fuel cell system shown in FIG. FIG. 5 is a diagram for explaining the operation of the valve provided in the vent pipe. FIG. 6 is a diagram for explaining the operation of the valve provided in the vent pipe. FIG. 7 is a diagram for explaining the operation of the valve provided in the vent pipe. FIG. 8 is a diagram for explaining the operation of the valve provided in the vent pipe.

One embodiment will be described below with reference to the drawings. First, the overall configuration of the fuel cell system will be described with reference to Figure 1.

As shown in FIG. 1, the fuel cell system 1 includes a fuel cell stack 10, a fuel gas supply system 30, a fuel gas exhaust system 35, an oxidant gas supply system 40, an oxidant gas exhaust system 45, a cooling water supply system 50, and a cooling water exhaust system 55. The fuel cell stack 10 generates electricity using hydrogen and oxygen. The fuel gas is hydrogen, and the oxidant gas is air.

The fuel gas supply system 30 includes a fuel gas supply source (not shown), such as a fuel gas tank, and a fuel gas supply pipe 31. The fuel gas supply pipe 31 connects the fuel gas supply source to the fuel cell stack 10. The fuel gas exhaust system 35 includes a fuel gas exhaust pipe 36. One end of the fuel gas exhaust pipe 36 is connected to the fuel cell stack 10.

The oxidant gas supply system 40 includes an oxidant gas supply source (not shown) such as a blower, and an oxidant gas supply pipe 41. The oxidant gas supply pipe 41 connects the oxidant gas supply source to the fuel cell stack 10. The oxidant gas exhaust system 45 includes an oxidant gas exhaust pipe 46. One end of the oxidant gas exhaust pipe 46 is connected to the fuel cell stack 10.

The cooling water supply system 50 includes a cooling water supply source 51 and a cooling water supply pipe 52. The cooling water supply pipe 52 connects the cooling water supply source 51 to the fuel cell stack 10. In the illustrated example, the cooling water supply source 51 is a cooling water tank. The top of the cooling water tank 51 is open to atmospheric pressure. The cooling water supply pipe 52 is connected to the bottom of the cooling water tank 51.

The cooling water discharge system 55 includes a cooling water discharge pipe 56 and a cooling water pump 57. One end of the cooling water discharge pipe 56 is connected to the fuel cell stack 10. In the illustrated example, the other end of the cooling water discharge pipe 56 is connected to the top of the cooling water tank 51. When the cooling water pump 57 is operated, the pressure in the cooling water discharge pipe 56 decreases, and the cooling water in the fuel cell stack 10 is discharged into the cooling water discharge pipe 56 and discharged into the cooling water tank 51.

In the example shown in Figures 1 to 3, the fuel cell stack 10 is a polymer electrolyte fuel cell stack. The fuel cell stack 10 includes a plurality of single cell batteries 11 and manifolds 21, 22, 23, 24, 25, and 26.

The multiple single cell batteries 11 are stacked in a direction perpendicular to the paper surface in Figs. 1 and 2 to form the stack 12. The stack 12 has a rectangular parallelepiped shape as a whole. The stack 12 has a first side 12a, a second side 12b, a third side 12c, and a fourth side 12d that extend along the stacking direction of the single cell batteries 11. The first side 12a and the second side 12b face each other. The third side 12c and the fourth side 12d face each other. The manifolds 21, 22, 23, 24, 25, and 26 are attached to the sides 12a, 12b, 12c, and 12d of the stack 12.

As shown in FIG. 3, each single cell battery 11 includes a membrane electrode assembly (MEA) 13, and a fuel separator 14 and an oxidizer separator 15 arranged on either side of the membrane electrode assembly 13. The membrane electrode assembly 13 includes a polymer electrolyte membrane 13a and a pair of electrodes (fuel electrode 13b and oxidizer electrode 13c) arranged on either side of the polymer electrolyte membrane 13a. The fuel separator 14 and the oxidizer separator 15 are made of a conductive porous material. The fuel separator 14 and the oxidizer separator 15 may be, for example, a conductive porous carbon plate.

A fuel gas flow path 16 is provided on the surface of the fuel separator 14 that contacts the membrane electrode assembly 13. One end of the fuel gas flow path 16 opens to the first side surface 12a of the stack 12. The other end of the fuel gas flow path 16 opens to the second side surface 12b of the stack 12.

An oxidizer gas flow channel 17 is provided on the surface of the oxidizer separator 15 that contacts the membrane electrode assembly 13. One end of the oxidizer gas flow channel 17 opens to the third side surface 12c of the stack 12. The other end of the oxidizer gas flow channel 17 opens to the fourth side surface 12d of the stack 12.

A cooling water flow path 18 is provided on the other surface of the fuel separator 14 or the other surface of the oxidizer separator 15. In the illustrated example, the cooling water flow path 18 is provided on the surface of the oxidizer separator 15. One end of the cooling water flow path 18 opens to the fourth side surface 12d of the stack 12. The other end of the cooling water flow path 18 opens to the third side surface 12c of the stack 12.

The fuel gas supply manifold 21 is provided facing the first side surface 12a of the stack 12. The internal space 21a of the fuel gas supply manifold 21 is connected to one end of the fuel gas flow path 16. In addition, a fuel gas supply pipe 31 is connected to the fuel gas supply manifold 21, and fuel gas is introduced into the internal space 21a through the fuel gas supply pipe 31.

The fuel gas exhaust manifold 22 is provided facing the second side surface 12b of the stack 12. The internal space 22a of the fuel gas exhaust manifold 22 is connected to the other end of the fuel gas flow path 16. In addition, a fuel gas exhaust pipe 36 is connected to the fuel gas exhaust manifold 22, and fuel gas is exhausted from the internal space 22a through the fuel gas exhaust pipe 36.

The oxidizer gas supply manifold 23 is provided facing the third side surface 12c of the stack 12. The internal space 23a of the oxidizer gas supply manifold 23 is connected to one end of the oxidizer gas flow path 17. In addition, an oxidizer gas supply pipe 41 is connected to the oxidizer gas supply manifold 23, and the oxidizer gas is introduced into the internal space 23a through the oxidizer gas supply pipe 41.

The oxidant gas exhaust manifold 24 is provided facing the fourth side surface 12d of the stack 12. The internal space 24a of the oxidant gas exhaust manifold 24 is connected to the other end of the oxidant gas flow path 17. In addition, an oxidant gas exhaust pipe 46 is connected to the oxidant gas exhaust manifold 24, and the oxidant gas is exhausted from the internal space 24a through the oxidant gas exhaust pipe 46.

The cooling water supply manifold 25 is provided facing the fourth side surface 12d of the laminate 12. The internal space 25a of the cooling water supply manifold 25 is connected to one end of the cooling water flow path 18. In addition, a cooling water supply pipe 52 is connected to the cooling water supply manifold 25, and cooling water is introduced into the internal space 25a through the cooling water supply pipe 52.

The cooling water discharge manifold 26 is provided facing the third side surface 12c of the laminate 12. The internal space 26a of the cooling water discharge manifold 26 is connected to the other end of the cooling water flow path 18. In addition, a cooling water discharge pipe 56 is connected to the cooling water discharge manifold 26, and the cooling water is discharged from the internal space 26a through the cooling water discharge pipe 56.

2, the flows of fuel gas, oxidant gas, and cooling water in the fuel cell stack 10 are shown by dashed arrows, dashed arrows, and solid arrows, respectively. As shown in FIG. 2, fuel gas is supplied from the fuel gas supply pipe 31 to the stack 12 through the internal space 21a of the fuel gas supply manifold 21. The fuel gas supplied to the stack 12 is introduced into the fuel gas flow path 16 of each single cell battery 11. The oxidant gas is supplied from the oxidant gas supply pipe 41 to the stack 12 through the internal space 23a of the oxidant gas supply manifold 23. The oxidant gas supplied to the stack 12 is introduced into the oxidant gas flow path 17 of each single cell battery 11. Then, the hydrogen in the fuel gas and the oxygen in the oxidant gas react in the single cell battery 11 to generate electricity and water. The fuel gas discharged from the fuel gas flow path 16 flows into the fuel gas discharge pipe 36 through the fuel gas discharge manifold 22. The oxidant gas discharged from the oxidant gas flow path 17 flows into the oxidant gas discharge pipe 46 through the oxidant gas discharge manifold 24.

The cooling water is supplied to the stack 12 from the cooling water supply pipe 52 through the cooling water supply manifold 25. The cooling water supplied to the stack 12 is introduced into the cooling water flow path 18 of each single cell battery 11 and is used to cool the single cell battery 11. The cooling water discharged from the cooling water flow path 18 flows into the cooling water discharge pipe 56 through the cooling water discharge manifold 26.

The illustrated fuel cell system 1 is configured so that when the cooling water pump 57 is operating, the pressure in the cooling water discharge pipe 56 is lower than the atmospheric pressure at least between the fuel cell stack 10 and the cooling water pump 57. As a result, in the fuel cell stack 10, the pressure in the cooling water flow path 18 is sufficiently lower than the pressure in the fuel gas flow path 16 and the oxidant gas flow path 17. As a result, the risk of the cooling water in the cooling water flow path 18 leaking into the fuel gas flow path 16 or the oxidant gas flow path 17 is effectively suppressed. In addition, the water generated at the oxidant electrode 13c moves from the oxidant electrode 13c through the porous gas diffusion layer and separator due to the above pressure difference into the cooling water flow path 18 and is removed outside the fuel cell stack 10.

However, the cooling water discharged from the fuel cell stack may contain air bubbles. If cooling water containing air bubbles is introduced into the cooling water pump, the pump's operating efficiency may decrease. As a result, cooling water may not be supplied sufficiently to the fuel cell stack, and the fuel cell stack may not be cooled sufficiently. If the fuel cell stack cannot be cooled sufficiently, the performance of the fuel cell may be impaired. To solve this problem, an air bleed valve is provided at the cooling water inlet of the cooling water pump to release the air bubbles in the cooling water into the atmosphere and suppress the introduction of air bubbles into the cooling water pump.

However, when the pressure in the cooling water discharge pipe is lower than atmospheric pressure, it is difficult to release the air bubbles in the cooling water into the atmosphere using the air bleed valve. For this reason, a special pump must be used as the cooling water pump. Such pumps are expensive, which increases the installation costs of the fuel cell system.

Taking these circumstances into consideration, the fuel cell system 1 of this embodiment is designed to allow the cooling water to be bled even when the pressure in the cooling water discharge pipe 56 is lower than atmospheric pressure.

Specifically, the vent pipe 60 is connected to the cooling water discharge pipe 56. The vent pipe 60 is connected to the cooling water discharge pipe 56 between the fuel cell stack 10 and the cooling water pump 57. The vent pipe 60 extends generally in the vertical direction. The lower end of the vent pipe 60 is connected to the cooling water discharge pipe 56. Air bubbles in the cooling water flowing through the cooling water discharge pipe 56 can be released outside the cooling water discharge system 55 via the vent pipe 60.

In the illustrated example, the cooling water discharge pipe 56 extends generally horizontally at the connection with the vent pipe 60. In other words, the cooling water discharge pipe 56 has a horizontal section 56a that extends generally horizontally between the fuel cell stack 10 and the cooling water pump 57, and the vent pipe 60 is connected to the horizontal section 56a. Air bubbles in the cooling water flowing through the cooling water discharge pipe 56 tend to move toward the upper half of the cooling water discharge pipe 56 in the horizontal section 56a. The vent pipe 60 is connected to the upper half of the horizontal section 56a. This allows air bubbles in the cooling water flowing through the horizontal section 56a to be efficiently captured in the vent pipe 60.

The cross-sectional area of the cooling water discharge pipe 56 is determined as follows. That is, the cross-sectional area of the cooling water discharge pipe 56 at the connection with the vent pipe 60 is determined to be larger than the cross-sectional area of the cooling water discharge pipe 56 at the connection with the fuel cell stack 10. As a result, the flow rate of the cooling water that flows from the fuel cell stack 10 into the cooling water discharge pipe 56 decreases at the connection between the cooling water discharge pipe 56 and the vent pipe 60. As a result, more air bubbles in the cooling water move upward at this connection. Therefore, more air bubbles in the cooling water can be captured in the vent pipe 60.

In the illustrated example, the horizontal portion 56a has an expanded portion 56b (see Figures 5 to 8). The cross-sectional area of the expanded portion 56b is larger than the cross-sectional area of the cooling water discharge pipe 56 other than the expanded portion 56b. The vent pipe 60 is connected to the upper half of the expanded portion 56b.

The cooling water tank 51 is located above the vent pipe 60. The upper end of the vent pipe 60 is connected to the bottom of the cooling water tank 51. A first on-off valve 61 is provided between the lower end and the upper end of the vent pipe 60. A second on-off valve 62 is provided between the lower end of the vent pipe 60 and the first on-off valve 61. The first on-off valve 61 is located above the second on-off valve 62. By having such a vent pipe 60 and on-off valves 61 and 62 in the fuel cell system 1, air bubbles in the cooling water flowing in the cooling water discharge pipe 56 can be efficiently discharged through the vent pipe 60. Specifically, by controlling the first on-off valve 61 and the second on-off valve 62 by a control method described with reference to Figures 4 to 8, air bubbles in the cooling water flowing in the cooling water discharge pipe 56 can be discharged through the vent pipe 60. In the illustrated example, the fuel cell system 1 has a control device 65 that controls the first on-off valve 61 and the second on-off valve 62.

The first on-off valve 61 and the second on-off valve 62 are not particularly limited as long as they are valves that can close/open the vent pipe 60 as needed. The first on-off valve 61 and the second on-off valve 62 may be, for example, solenoid valves.

The control method of the fuel cell system 1 will be described with reference to Figures 4 to 8. The following mainly describes the control method of the first on-off valve 61 and the second on-off valve 62. In Figures 5 to 8, the cooling water supply pipe 52 is omitted for simplicity.

When power generation by the fuel cell system 1 is started, first, the first on-off valve 61 and the second on-off valve 62 are opened in response to a control signal from the control device 65. This causes the cooling water in the cooling water tank 51 to flow into the vent pipe 60, filling the vent pipe 60 with cooling water (step S1 in FIG. 4).

Next, as shown in FIG. 5, in response to a control signal from the control device 65, the first on-off valve 61 is closed while the second on-off valve 62 remains open (step S2 in FIG. 4). This prevents the area of the vent pipe 60 below the first on-off valve 61 from being affected by atmospheric pressure through the cooling water tank 51. Hereinafter, the state in which the first on-off valve 61 is closed and the second on-off valve 62 is open is also referred to as the "first state."

Next, the supply of fuel gas, oxidant gas, and cooling water to the fuel cell stack 10 is started. The supply of cooling water to the fuel cell stack 10 is performed by operating the cooling water pump 57 to reduce the pressure in the cooling water discharge pipe 56. In the illustrated example, the pressure in the cooling water discharge pipe 56 is made lower than atmospheric pressure at least between the fuel cell stack 10 and the cooling water pump 57. As a result, the pressure in the cooling water flow path 18 of the fuel cell stack 10 is also sufficiently reduced, and cooling water is supplied from the cooling water tank 51 to the cooling water flow path 18. In addition, the cooling water in the fuel cell stack 10 is discharged to the cooling water discharge pipe 56. Then, the cooling water flowing in the cooling water discharge pipe 56 is discharged to the cooling water tank 51 through the cooling water pump 57. In this way, the cooling water circulates through the cooling water supply system 50, the fuel cell stack 10, and the cooling water discharge system 55.

Air bubbles in the cooling water flowing through the cooling water discharge pipe 56 rise within the cooling water discharge pipe 56 and are captured in the air vent pipe 60 that opens into the cooling water discharge pipe 56. The air bubbles captured in the air vent pipe 60 accumulate in the area of the air vent pipe 60 between the first opening/closing valve 61 and the second opening/closing valve 62.

Next, when a certain amount of gas has accumulated in the degassing pipe 60 after a certain time has elapsed since the first and second on-off valves 61 and 62 were put into the first state (YES in step S4 in FIG. 4), as shown in FIG. 6, the second on-off valve 62 is closed while the first on-off valve 61 is kept closed in response to a control signal from the control device 65 (step S5). Here, the above-mentioned certain time may be a time length that does not allow too much gas to accumulate in the degassing pipe 60. For example, it may be a time length that allows the amount of gas captured in the degassing pipe 60 to be contained in the area between the first on-off valve 61 and the second on-off valve 62 of the degassing pipe 60. Hereinafter, the state in which both the first on-off valve 61 and the second on-off valve 62 are closed is also referred to as the "intermediate state."

Next, as shown in FIG. 7, in response to a control signal from the control device 65, the first on-off valve 61 is opened while the second on-off valve 62 is closed (step S6). As a result, the air bubbles trapped in the area between the first on-off valve 61 and the second on-off valve 62 rise and are released into the cooling water tank 51, and at the same time, the cooling water in the cooling water tank 51 is introduced into the area above the second on-off valve 62 in the degassing pipe 60. Note that, since the second on-off valve 62 remains closed while the first on-off valve 61 is open, the area below the second on-off valve 62 in the degassing pipe 60 is prevented from being affected by atmospheric pressure through the cooling water tank 51. Therefore, the air bubbles in the cooling water flowing through the cooling water discharge pipe 56 continue to be trapped in the degassing pipe 60. Hereinafter, the state in which the first on-off valve 61 is open and the second on-off valve 62 is closed is also referred to as the "second state".

Next, as shown in FIG. 8, in response to a control signal from the control device 65, the first on-off valve 61 is closed while the second on-off valve 62 remains closed (step S7). That is, the first on-off valve 61 and the second on-off valve 62 are placed in an intermediate state.

Next, as shown in FIG. 5, in response to a control signal from the control device 65, the second on-off valve 62 is opened while the first on-off valve 61 is closed (step S8). That is, the first on-off valve 61 and the second on-off valve 62 are set to the first state. By keeping the first on-off valve 61 closed while the second on-off valve 62 is open, the area of the vent pipe 60 below the first on-off valve 61 is prevented from being affected by atmospheric pressure through the cooling water tank 51. Therefore, air bubbles in the cooling water flowing through the cooling water discharge pipe 56 continue to be trapped in the vent pipe 60. The air bubbles (gas) trapped in the vent pipe 60 accumulate in the area of the vent pipe 60 between the first on-off valve 61 and the second on-off valve 62.

If power generation by the fuel cell system 1 continues, the supply of fuel gas, oxidant gas, and cooling water to the fuel cell stack 10 continues. Therefore, the operation of the cooling water pump 57 also continues. If the operation of the cooling water pump 57 continues in step S9 (YES in step S9), the process returns to step S4 and control of the first opening/closing valve 61 and the second opening/closing valve 62 continues.

On the other hand, when power generation by the fuel cell system 1 is terminated, the supply of fuel gas, oxidant gas, and cooling water to the fuel cell stack 10 is stopped. Therefore, the operation of the cooling water pump 57 is also stopped. When the operation of the cooling water pump 57 is stopped, no more cooling water is introduced into the cooling water pump 57. Therefore, if the operation of the cooling water pump 57 is not continued in step S9 (NO in step S9), the control of the first opening/closing valve 61 and the second opening/closing valve 62 is terminated.

Also, in step S4, if the certain time has not elapsed (NO in step S4), the process returns to step S4.

In the above-described embodiment, the separator 15 provided with the cooling water flow path 18 is made of a porous material, but this is not limited thereto. The separator 15 provided with the cooling water flow path 18 may be made of a material that does not allow water to pass through, such as a metal plate. In this case, too, the pressure in the cooling water discharge pipe 56 may be made lower than atmospheric pressure in order to prevent the cooling water from leaking from the cooling water supply system 50 or the cooling water discharge system 55, which may cause problems similar to those described above.

In the above-described embodiment, the first on-off valve 61 and the second on-off valve 62 are switched to the intermediate state after a predetermined time has elapsed since they were switched to the first state, but this is not limited to the above. The first on-off valve 61 and the second on-off valve 62 may be switched to the intermediate state after a predetermined amount of gas has accumulated in the vent pipe 60 after being switched to the first state. In this case, a liquid level gauge or a level sensor (a level switch or a level gauge) that measures the water level of the cooling water in the vent pipe 60 may be provided in the vent pipe 60, and the first state may be switched to the intermediate state based on the measurement results from the liquid level gauge or the level sensor.

In addition, in the above-described embodiment, the first on-off valve 61 and the second on-off valve 62 are controlled using the control device 65, but this is not limited to the above. The first on-off valve 61 and the second on-off valve 62 may be controlled manually.

In addition, in the above-described embodiment, the upper end of the vent pipe 60 is connected to the cooling water tank 51 included in the cooling water supply system 50, but this is not limited to the above. The upper end of the vent pipe 60 may be connected to a cooling water tank other than the cooling water tank 51 of the cooling water supply system 50. When the vent pipe 60 is connected to the cooling water tank 51 of the cooling water supply system 50, the fuel cell system 1 can be made smaller than when the vent pipe 60 is connected to a cooling water tank other than the cooling water tank 51.

As described above, the fuel cell system 1 according to the present embodiment includes a fuel cell stack 10 that generates electricity using hydrogen and oxygen, a cooling water discharge pipe 56 connected to the fuel cell stack 10, and a cooling water pump 57 that discharges cooling water from the fuel cell stack 10 through the cooling water discharge pipe 56. During operation of the cooling water pump 57, the pressure in the cooling water discharge pipe 56 is lower than atmospheric pressure at least between the fuel cell stack and the cooling water pump 57. In addition, a vent pipe 60 that extends generally vertically is connected to the cooling water discharge pipe 56 between the fuel cell stack 10 and the cooling water pump 57. According to this fuel cell system 1, air bubbles in the cooling water flowing through the cooling water discharge pipe 56 can be discharged through the vent pipe 60 before the cooling water is introduced into the cooling water pump 57.

In addition, in the fuel cell system 1 according to this embodiment, the cooling water discharge pipe 56 extends generally horizontally at the connection with the vent pipe 60. The vent pipe 60 is connected to the upper half of the cooling water discharge pipe 56. This allows air bubbles in the cooling water flowing through the cooling water discharge pipe 56 to be efficiently discharged through the vent pipe 60.

In addition, in the fuel cell system 1 according to this embodiment, the cross-sectional area of the cooling water discharge pipe 56 at the connection with the vent pipe 60 is larger than the cross-sectional area of the cooling water discharge pipe 56 at the connection with the fuel cell stack 10. This allows more air bubbles in the cooling water flowing through the cooling water discharge pipe 56 to be discharged through the vent pipe 60.

In the fuel cell system 1 according to this embodiment, the lower end of the vent pipe 60 is connected to the cooling water discharge pipe 56. The upper end of the vent pipe 60 is connected to the cooling water tank 51. A first on-off valve 61 is provided between the upper and lower ends of the vent pipe 60. A second on-off valve 62 is provided between the lower end of the vent pipe 60 and the first on-off valve 61. Since the fuel cell system 1 has such vent pipe 60 and on-off valves 61, 62, air bubbles in the cooling water flowing through the cooling water discharge pipe 56 can be efficiently discharged through the vent pipe 60.

Specifically, the first on-off valve 61 and the second on-off valve 62 transition from a first state in which the first on-off valve 61 is closed and the second on-off valve 62 is open, through an intermediate state in which the first on-off valve 61 and the second on-off valve 62 are both closed, to a second state in which the first on-off valve 61 is open and the second on-off valve 62 is closed, thereby removing air bubbles in the cooling water flowing through the cooling water discharge pipe 56.

The fuel cell system 1 according to this embodiment further includes a cooling water supply pipe 52 having one end connected to the fuel cell stack 10 and the other end connected to the cooling water tank 51. In other words, the vent pipe 60 is connected to the cooling water tank 51 of the cooling water supply system 50. In this case, the fuel cell system 1 can be made smaller than when the vent pipe 60 is connected to a cooling water tank other than the cooling water tank 51.

In addition, in the fuel cell system 1 according to this embodiment, the first on-off valve 61 and the second on-off valve 62 are switched to the intermediate state after the first state is maintained for a predetermined time. This prevents too much gas from accumulating in the vent pipe 60.

Alternatively, in the fuel cell system 1 according to this embodiment, the first on-off valve 61 and the second on-off valve 62 are switched to the intermediate state after the first state is maintained until a predetermined amount of gas accumulates between the lower end of the vent pipe 60 and the first on-off valve 61. This also prevents too much gas from accumulating in the vent pipe 60.

In the fuel cell system 1 according to the present embodiment, the fuel cell stack 10 includes a membrane electrode assembly 13 including a polymer electrolyte membrane 13a, a fuel electrode 13b and an oxidizer electrode 13c arranged on both sides of the polymer electrolyte membrane 13a, and a fuel separator 14 and an oxidizer separator 15 arranged on both sides of the membrane electrode assembly 13. A fuel gas flow path 16 is provided on one side of the fuel separator 14. An oxidizer gas flow path 17 is provided on one side of the oxidizer separator 15. A cooling water flow path 18 is provided on the other side of the fuel separator 14 or the oxidizer separator 15. The separator provided with the cooling water flow path 18 is made of a porous material. In such a fuel cell system 1, when the pressure in the cooling water discharge pipe 56 is made lower than the atmosphere, the pressure in the cooling water flow path 18 in the fuel cell stack 10 becomes sufficiently lower than the pressure in the fuel gas flow path 16 or the oxidizer gas flow path 17. As a result, the risk of the cooling water in the cooling water flow passage 18 leaking into the fuel gas flow passage 16 or the oxidant gas flow passage 17 is effectively suppressed. In addition, the water generated at the oxidant electrode 13c moves from the oxidant electrode 13c through the porous gas diffusion layer and separator due to the pressure difference described above to the cooling water flow passage 18, and is removed outside the fuel cell stack 10.

Although the embodiments and some variations of the present invention have been described, these embodiments and variations are presented as examples and are not intended to limit the scope of the invention. These new embodiments and variations can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and variations are included within the scope and gist of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Naturally, these embodiments and variations can also be combined in part as appropriate within the gist of the invention.

1: fuel cell system, 10: fuel cell stack, 12: stack, 30: fuel gas supply system, 31: fuel gas supply piping, 35: fuel gas exhaust system, 36: fuel gas exhaust piping, 40: oxidant gas supply system, 41: oxidant gas supply piping, 45: oxidant gas exhaust system, 46: oxidant gas exhaust piping, 50: cooling water supply system, 51: cooling water tank, 52: cooling water supply piping, 55: cooling water exhaust system, 56: cooling water exhaust piping, 57: cooling water pump, 60: vent piping, 61: first on-off valve, 62: second on-off valve, 65: control device

Claims (8)

a fuel cell stack that generates electricity using hydrogen and oxygen;
a cooling water discharge pipe connected to the fuel cell stack;
a cooling water pump that discharges cooling water from the fuel cell stack through the cooling water discharge pipe;
Equipped with
During operation of the cooling water pump, the pressure in the cooling water discharge pipe is lower than atmospheric pressure at least between the fuel cell stack and the cooling water pump;
a vent pipe extending generally in a vertical direction between the fuel cell stack and the cooling water pump is connected to the cooling water discharge pipe,
The lower end of the vent pipe is connected to the cooling water discharge pipe,
The upper end of the vent pipe is connected to a cooling water tank,
A first on-off valve is provided between the lower end and the upper end of the vent pipe,
a second on-off valve is provided between a lower end of the vent pipe and the first on-off valve , The cooling water discharge pipe extends substantially horizontally at a connection portion with the air vent pipe,
2. The fuel cell system according to claim 1, wherein the ventilation pipe is connected to an upper half of the cooling water discharge pipe. 3. The fuel cell system according to claim 1 , further comprising a cooling water supply pipe having one end connected to said fuel cell stack and the other end connected to said cooling water tank. 4. The fuel cell system according to claim 1, wherein the first and second on-off valves transition from a first state in which the first on-off valve is closed and the second on-off valve is open, through an intermediate state in which the first and second on-off valves are both closed, to a second state in which the first on- off valve is open and the second on-off valve is closed, thereby removing air bubbles in the cooling water flowing through the cooling water discharge piping. 5. The fuel cell system according to claim 4 , wherein the first and second on-off valves are switched to the intermediate state after the first state is maintained for a predetermined time. 5. The fuel cell system of claim 4, wherein the first and second opening/closing valves are switched to the intermediate state after the first state is maintained until a predetermined amount of gas accumulates between the lower end of the vent pipe and the first opening/closing valve. 7. The fuel cell system according to claim 1 , further comprising a control unit that controls opening and closing of the first on-off valve and the second on-off valve . The fuel cell stack comprises:
A membrane electrode assembly including a polymer electrolyte membrane and a fuel electrode and an oxidizer electrode disposed on either side of the polymer electrolyte membrane;
a fuel separator and an oxidant separator disposed on either side of the membrane electrode assembly;
Including,
A fuel gas flow path is provided on one surface of the fuel separator,
an oxidant gas flow channel is provided on one surface of the oxidant separator;
a cooling water flow path is provided on the other surface of the fuel separator or the oxidizer separator;
8. The fuel cell system according to claim 1, wherein the separator provided with the cooling water flow passage is made of a porous material.

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